1. Field of the Invention
In a number of scientific disciplines, radioactive materials are detected by autoradiography, a process wherein the substrate is placed in superposition over a piece of X-ray film and the radiation "exposes" the silver halide. Sometimes this is enhanced by using a phosphor screen behind the film. Sometimes it is done at low temperature to increase sensitivity.
A common need is a means of marking the substrate in order for the researcher to be able to clearly identify his system and, very importantly, to facilitate proper match up of the areas on the substrate with their corresponding exposed areas on the film.
Most research laboratories achieve this by preparing some sort of radioactive marker; these usually take the form of a colored ink to which is added appropriate amounts of outdated radiolabeled materials. Application is often by adaptation of commercial pens or simple dotting devices.
The disadvantages of this are many including:
1. Leakage can lead to general, although low level contamination. PA0 2. Multiple pens must be prepared as it is necessary to approximate the amount of radioactivity in the substrate. In addition, it is necessary in many cases to match the particular radionuclide under study. PA0 3. The intensity of marking actually attained on the film is dependent not only upon time of exposure and radionuclide energy, but also is affected by the plastic overlays commonly used and, in some special cases, temperature. PA0 4. There is significant potential for "abuse" in that a convenient pen will potentially migrate from the laboratory.
The present invention relates to a process for the labeling of materials to be autoradiographed using a phosphorescent material, such as an ink effectively avoiding all of the radioactivity associated disadvantages cited above. In the Examples below, this is achieved by the use of a carefully selected phosphor with decay time adequate to allow convenient and effective application.
2. Prior Art
U.S. Pat. No. 2,396,219 discloses a phosphorescent marking crayon using a zinc-cadmium activated by copper phosphor.
U.S. Pat. No. 3,631,243 discloses a device for marking indicia on photographic film in a housing involving insertion into and withdrawal from the housing a unit bearing the indicia and a phosphorescent source of light to expose the film.